There are various methods for producing HFO-1234yf, which shows great promise as a refrigerant for car air conditioners, etc., because of its low global warming potential (GWP). For example, PTL 1 discloses a production process in which HF in an amount exceeding the stoichiometrically required amount is supplied to a reaction starting raw material (CCl3CF2CH3). Further, PTL 2 discloses a production process in which fluorocarbon (CF3CFHCFH2) is dehydrofluorinated. In these processes, the outflow from the reactor is a mixture of the desired product HFO-1234yf and HF present in an amount at least equimolar to that of HFO-1234yf.
To remove HF from a mixture of HFO-1234yf and HF in order to obtain a purified product of HFO-1234yf, the mixture of HFO-1234yf and HF is treated so that HF is absorbed by water or alkali, which is known as a general method for removing HF from a mixture of an organic substance and HF. However, this method requires a large quantity of water or alkali, leading to the discharge of a large amount of industrial waste. Thus, this method is not beneficial in terms of environmental preservation and production cost. In another generally known method for removing HF, H2SO4 is used to collect HF as a fluorosulfuric acid. In this method, however, the fluorosulfuric acid that is generated is highly corrosive, and the materials of equipment used are therefore limited to highly corrosion-resistant materials, leading to an increase in production cost. Furthermore, in this HF-removing method, reuse of the removed HF in the reaction (recycling use) requires a high level of technology, leading to an increase in production cost when the collected HF is either recycled or disposed.
The processes described below resolve these problems. For example, PTL 3 discloses a process in which a mixture of HFO-1234yf and HF is distilled, and an azeotropic mixture of HFO-1234yf and HF is extracted from the top of a distillation column, while HFO-1234yf is obtained from the bottom of the distillation column. This process requires a larger distillation column because it is necessary to extract a large amount of HFO-1234yf together with HF from the top of the column. Moreover, even when employing a process in which the azeotropic mixture is recycled, the circulation of a large amount of an HFO-1234yf and HF mixture requires that large equipment be used in the process, leading to increases in equipment and operating costs. Further, for example, PTL 4 discloses a process in which a mixture of HF and HFO-1234yf is subjected to azeotropic distillation, the outflow is liquefied by cooling, followed by liquid-liquid separation, and each liquid is distilled, thereby separating HFO-1234yf and HF. In this process, it is necessary to repeat heating a large amount of separated product, followed by cooling and heating again in the separation step, resulting in a large level of energy consumption and increasing the operating cost.